1. Field of the Invention
The invention concerns electron tubes.
For a clear understanding of the invention, we shall give a more precise description of its application to a cathode-ray tube, namely a tube comprising, firstly, an electron gun producing an electron beam and, secondly, a luminescent screen reacting to the impact of the beam to produce a light image.
2. Description of the Prior Art
A cathode-ray tube is formed, generally speaking, by a glass bulb in which the different elements (and notably the different electrodes) enabling the operation of the tube are placed. A high vacuum is then set up in the bulb.
The glass bulb is formed by four different main parts which are respectively:
the screen or front face of the tube, forming the luminescent screen on to which the electron beam is directed;
the cone, in which the electron beam moves; the wide part of the cone ends on the front face; the narrow part is connected to the neck of the bulb;
The neck, which is a glass tube with a small diameter as compared with the dimensions of the front face; in the cone, there are placed chiefly the electron gun with the beam focusing electrodes; coils for the angular deflection of the beam are placed around the neck;
the stem which, in practice, is an end glass plate enclosing the neck on the side opposite the tube; this plate is crossed by connection terminals enabling electrical connection between each of the electrodes internal to the tube and the exterior; the crossings are vacuum tight; the stem generally comprises a pip to set up the vacuum by pumping.
The stem, after the assembly of the internal elements of the tube, is soldered to the neck by a glass/glass soldering operation, i.e. by melting the glass of the stem and the glass of the neck, using a torch.
In the prior art, the electrodes of the electron gun are supported by metallic points embedded in glass rods extending, in the neck, to its periphery, in a direction parallel to the axis of the neck. The metallic points are embedded in the glass rods by prior heating of these rods to a temperature which gives the glass a paste-like consistency. These points are, moreover, soldered to the periphery of the electrodes which they have to support.
The different potentials needed for the working of the electrodes are conveyed either by the connection terminals of the stem or, for certain electrodes, by springs in indirect contact (through a graphite layer deposited on the internal wall of the neck and the cone) with the front face of the bulb.
Other springs are designed to center the gun in the neck, to hold it and to make it resistant to vibrations.
On the left-hand side of FIG. 1, a standard cathode-ray tube assembly of this type is shown. Only the stem (at the bottom of the figure) and the neck are shown. The cone and the front face are not shown. They would extend towards the top of the figure.
The stem is designated by the reference 10, the neck by the reference 12, the solder between the stem and the neck by 14, connection terminals going through the stem by 16, internal glass rods by 18, electrode supporting points by 20, electrodes by G1, G2, G3, G4 and the pumping pip by 22.
It will be noted that the right-hand part of FIG. 1 represents not the prior art but the invention.
Besides, elements external to the tube, such as the electromagnetic coils used to deflect the electron beam, have not been shown. These coils surround the neck so as to act on the trajectory of the electrons between the electron gun and the end of the neck.
It is an aim of the invention to make electron tubes that are less bulky widthwise and/or lengthwise.
Another aim is to make tubes in which the energy consumption of the deflection coils is reduced to the minimum.
Another aim of the invention is to maximize the diameter of the electrostatic focusing electrodes in the allocated space within the neck, in order to reduce spherical aberrations to the minimum.
Another aim is to increase the general sturdiness of the tube.
Yet another aim is to minimize the risks of production of solid particles inside the tube during fabrication or during operation, as these particles could damage the quality of operation of the tube (the quality of the image for example).
Finally, an aim of the invention is to prevent any chemical pollution of certain sensitive elements such as the screen of the tube or the cathode of the electron gun by products such as water vapor or other elements resulting from combustion in a torch used to solder or heat certain parts of the tube.